Return bend



March 19, 1935. A. T. DUDLEY RETURN BEND Filed Dec. 19, 1950 Her-1* A 2 7 I a w INVENTOR Patented Mar. 19, 1935 RETURN BEND Andrew T. Dudley, Port Arthur, Tex., assignor to The Texas Company, poration of Delaware New York, N. Y., a cor- Application December 19, 1930, Serial No. 503,415

8 Claims.

This invention relates to pipe stills or tubular heating systems, and particularly to a return bend assembly for pipe coils and the like, used for heating fluids in practicing processes involving high temperatures and pressures, as, for example,

in the conversion of hydrocarbon oils where the material subjected to heat treatment is passed at a high velocity through a series of interconnected tubes.

In heating systems wherein the fluid to be heated is passed through a tubular coil located within a furnace, difficulty has been experienced in designing an apparatus capable of withstanding the shock of certain changes in temperature to which it is subjected, and the resulting expansion and contraction of the metals making up its composition. The problem is especially acugze an arrangements wherein a plurality of tubes, connected by return bends, extend substantially parallel through a furnace and carry decomposable substances such as hydrocarbon oils. In the latter instances, it is usually necessary to provide removable elements which can be readily de-. tached from the ends of the tubes to allow access to the interior thereof for cleaning purposes. Furthermore, these removable bends or couplings usually have the burden of compensating for unequal movements within the various tubes making up the integral parts of the coil as well as providing joints that arenon-leakable and otherwise serviceable under the severe operating conditions which are imposed upon them.

Heretofore, the efforts of designers or inventors in solving the problem of providing satisfactory return bends have been directed toward rigidity of design and construction. 'Apparently prior workers in the art have held to the idea that the solution of the problem resided in the selection of bends of proper size and strength, having sufficient rigidity to withstand the forces exerted thereon without failure. The result has been that materials stifi and inflexible in character, cumbersome and massive in construction, have been produced which are either sufliciently strong to hold their shape, or which on yielding almost invariably spring a leak.

The present invention contemplates a return bend assembly which will overcome the difficulties heretofore touched upon, by providing an arrangement which is not dependent for its success upon the rigidity and non-yielding strength of the return bend to withstand the abuse imposed upon it, but rather aims at the design of a structure whereby flexibility and freedom of movement between the integral parts are, relied upon to absorb the stresses and to allow the supporting parts to assume new positions without imposing undue strain upon any single element. Such an arrangement is conveniently obtained in accordance with the invention, partially by providing ball and socket joints between the tubes and the bend, the arrangement being such that a ball and socket movement is permitted between the contacting parts of the joints. The arrangement is further accomplished by holding the ball and socket joints together with removable fastenings capable of limited adjustment and likewise providing the adjustment of said fastenings with ball and socket joints whereby freedom of movement of the return bend within the fastenings is assured without cramping or straining individual parts of the assembly.

The invention will be more clearly. understood by reference to the accompanying drawing considered together with the following description which illustrates and describes a preferred embodiment thereof.

In the drawing: I

Fig. 1 is a plan view with parts in section of a return bend assembly constructed in accordance with the invention.

Fig. 2 is a sectional view of the return bend assembly taken on the line 2-2 of Fig.1 looking in the direction of the arrows.

Fig. 3 is a view partly in section of the assembly after the removable fastenings or clamping members areremoved, and the return bend dislodged from the tubes.

Fig. 4 is a detail of one of the clamping members.

Fig. 5 is a view partly in section of a crossbar and adjustable screw or threaded bolt for holding the return bend in place.

Referring to the drawing, the return bend assembly comprises a curved body forming a conduit or a return bend member 10, adapted to fit on the end of a pair of adjacent tubes 11, and held securely in place by removable fasteners or clamping members 12 and cross-bar 13. The drawing is intended as illustrative of the manner of joining or clamping the ends of a pair of tubes, it being understood that any number of tubes may comprise the tubular coil, each extending through or into the furnace with the ends connected. The invention is particularly applicable to coils in which the tubes are arranged in a vertical position with the ends of adjacent tubes connected, the several tubes beingsupported at their upper ends whereby the expansion which occurs in them is reflected in a downward projection. However, the invention is also applicable to other arrangements in which the tubes may assume longitudinal or other positions in arranging the tubular coil within the furnace.

The tubes are provided with enlarged portions or collars 15 (Fig. 3)" at the ends thereof, machined to form suitable joints with the return bend and also to provide a shoulder, rim or collar behind which the clamping members may fit. The curved, beveled or spherical faces 16 of the enlarged portion fits snugly into flaring or beveled mouths or ends 17 of the return bend to form a flexible joint of the ball and socket type.

The removable fasteners or clamping members 12, a detail of one being shown in Fig. 4, comprise a semi-circular portion 20, provided with a shoulder or offset portion 21 to fit behind the enlarged portions 1.5 of the tubes and with cars 22 perforated at 23, to engage stud bolts. A pair of companion clamping members are adapted to form clasps or split rings or split cylinders and to encircle the tubes 11 immediately behind the enlarged portions so that one of the edges of the enlarged portions or collars rest on the shoulders 21. The clamping members also comprise projecting members or shanks 24, the outer or extending end of which are provided with slots or recesses 25 to engage the outer ends of the cross-bar 13 hereinafter described. The projecting members or shanks 24 are in alignment with the tubes when the clamps are in place, which can be more readily observed in Fig. 1. The clamping members are also equipped with projecting members or lugs 26, extending laterally therefrom, to engage a web portion of the return bend referred to hereinafter.

The return bend 10 (Fig. 3) is shown for convenience as approximately semi-circular in shape with the ends in approximately the same plane so as to join or couple two parallel tubes. However, such a construction is merely arbitrary in the drawing and the invention is equally applicable to other shapes and forms such as elbows, distorted angular bends and other variations in curvature and shapes of a coupling or return bend suitable to join ends of adjacent tubes of a tubular coil. The bend is provided with spherical or ground valve faces 17 to engage with the ends of the tubes as mentioned heretofore. A web 30 joins the concave surface of the bend and projects a short distance beyond the flaring ends 17 thereof to fit between the projections or lugs 26 of the clamping members as shown in Figs. 1 and 2. The return bend is also provided with a pair of projecting members or lugs 31 on the convex surface, one of which is in alignment with each of the tubes 11 when the bend is in place. The ends of the projections or lugs 31 are slightly cupped, forming cavities to receive the ends of the threaded cross-bar bolts 37. The bottoms 32 of the lugs are convex to provide beaded or ball-shaped support for the cross-bar bolts.

The cross-bar arrangement (Fig. 5) comprises an elongated cross-bar 13, provided with projecting members or hooks 36 at the ends to fit into the recesses 25 of the clamping members. The cross-bar 13 is enlarged at the middle to permit a bore or threaded hole therein for engaging the cap screw or threaded bolt 3'7. The end of the bolt 37 is slightly concave, forming a socket 38 to fit over the convex bottoms 32 of the lugs on the return bends. One of the cross-bar arrangements fits between each pair of clamping members as shown in Fig. 2, thereby permitting the screw bolts to be screwed down on each of the lugs 31 of the return bend. While a definite structure of the cross-bar arrangement is shown for purposes of convenience in illustrating the 12 together with the cross-bar assembly may be constructed as a. single unit, whereby the crossbar is conceived as being stationary instead of removable. In this way, the clamping members and cross-bar form a clamping device which folds over the convex surface of the return bend and clasps the ends of the tubes to bind the return bend securely to the tubes with the aid of the cap screw, if desired.

In assembling a return bend arrangement such as the one illustrated in the drawing, referring first to Fig. 3, the beveled ends 16 of the tubes 11 and the concave faces 1'? of the return bend are cleaned free of carbon or other adhering solid material. The return bend is then fitted to the ends of the tubes making ball and socket type of joints. A pair of clamps consisting of a member such as illustrated in Fig. 4 and a companion member are clamped to the ends of each tube in such a way that the split rings or. cylinders, made up of the semi-annular portions 20, fit around the end of tubes with the collars 15 resting on the shoulders 21. The clamps are then tightened by means of stud bolts 40, which fit into the perforated cars 22 as better shown in Fig. 2.

It will be observed from Figs. 1 and 2 that the web 30 joining the inner semi-circular portions of the return bend fits snugly between the four lugs 26 of the clamps when the two pair of clamps are drawn together around the tubes. The purpose of this arrangement is to facilitate the alignment or centering of the return bend in relation to the tubes and furthermore to prevent rotation of the bend which would result in a misalignment and improper fit of the ball and socket joints between the return bend and the ends of the tubes.

After the return bend and clamps have been properly located and the stud bolts tightened sufficiently to secure the parts in relation to each other, the cross-bars are slipped into place as shown in Fig. 2. The cross-bars 13 fit into the recesses 25 of the clamps and the hooked ends 36 penetrate the recesses and curve slightly upward along the outside of the shank 24 to lock the cross-bars in place. The screws 37 are next threaded into the cavity or cups of the lugs 31 and the sockets 38 on the ends thereof screwed down on the ball-shaped bottoms 32 of the lugs, to provide ball and socket type of joints. By tightening the screws the bend 10 is set firmly against the ends of the tube.

As a variation in the method of assembling the return bend arrangement, the clamping devices might well be assembled in advance and folded over the convex surface of the return bend prior to clasping the split rings 20 to the ends of the tubes. In this way, the return bend would be placed on the ends of the tubes, then the crossbar and clamping members 12 assembled and folded over the return bend and the split rings 20 clasped about the ends of the tubes. The stud bolts 40 would be inserted and drawn tight, simultaneously centering the mouths of the return bend in relation to the ends of the tubes. Finally the screw bolt 37 would be screwed down to press the ends of the bend tightly to the tubes. Such a variation in method of assembling the apparatus would be particularly applicable in the type of, clamping devices wherein the clamping members 12 and the cross-bar 13 were constructed in a. single unit as suggested heretofore.

In fitting up a tubular heater, the work is usually done when the various parts are cold. When the fluid is started moving through the tubes and the furnace fires or other heating means are turned on, the parts begin to warm up and expand in proportion to the rise in temperature. In most cases the ends of the tubes project through supporting tube sheets and the return bends are situated outside of the heated zone. The return bends may be insulated or closed in from the cooling efiects of the atmosphere by appropriate doors or shutters, whereby the tubes are heated by the furnace heat and the return bend parts are heated by the hot oil passing through them rather than by the heat from the furnace. Since the tubes are normally much hotter than the oil passing therein, the return bends are at a lower temperature which naturally causes an unequal expansion between the tubes and the bends. Likewise the tubes and bend will expand more rapidly than the clamps, cross-bars and screw bolts. This unequal expansion, which normally causes considerable trouble in rigid joints, has been found to be an advantage with my improved assembly, in that the greater expansion and resulting lengthening of the tubes serves to tighten the clamp and secure the return bend more tightly to the ends of the tubes.

A special advantage of the return bend assembly of the invention is in the ball and socket type of joints. The employment of these joints between the return bend and the tubes, as well as a similar type for the contacts between the screw bolts 37 and lugs 31 upon the outer convex surface of the bend, provide for a slight rolling or sliding movement in the joints to absorb stresses thereon, and to permit the parts to adjust themselves to new positions of less strain whenever unequal expansion of the parts occur, or other movement takes place among the integral parts of the tubular system. In this way the sagging of an invidual tube or a slightly lateral movement by adjacent tubes, causing spreading with relation to one another, is readily taken care of by movements within the joints with no excessive strain upon any individual part of the'assembly. It is preferable that the curved surfaces 16 of the ends of the tubes and the cooperating seats 17 on the ends of the bend as well as the curved surfaces 32 of the lugs 31 are concentric; that is, the radii of the spherical joints between the two bends and the mouths or termini of the return element and the convex seats 32 upon which the securing cap screws 3'7 rest, have the same center. Due to the flexibility thereby provided, a rocking or rolling of the surfaces 16 of the tubes in the seats 17 of the bend and a corresponding movement of the cap-screw ends 38 upon the convex seats 32 may occur without increasing or decreasing stresses developed in making the bends tight on the tube ends.

With respect to the construction of the return bend assembly, a number of parts may be dropforged from steel because of the simplicity of their design. The advantage of drop-forged parts is well known in the art, particularly as regards their toughness, that is, their strength and resilience. Furthermore, it is not necessary to choose so carefully the kinds of materials of which the diiferent parts or contiguous parts are to be made with respect to the coefilcient' of expansion of the metals. This has a peculiar advantage in the pressure cracking of certain petroleum fractions parts of materials having about the same coefli-,

cient of expansion in order to avoid injury due to unequal expansion. In choosing materials for the manufacture of my return bend, the different parts may be of any desirable alloy since the expansion thereof is automatically adjusted to relieve the strain.

Obviously many modifications and-variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A return bend assembly for pipe stills comprising a curved body forming a conduit, said curved body'having a webprojecting from the concave surface thereof, clamping devices adapted to fold over and to bind said curved'body to a pair of tubes, lugs on said clamping devices extending laterally therefrom to engage said web and to hold the mouths of the conduit substantially in alignment with the ends of the tubes.

2. In a return bend assembly for pipe stills in which a return bend interconnects a' pair of adjacent tubes to form a continuous coil, said tubes having enlarged collar-like portions at the end thereof, clamping devices for holding the return bend to the tubes comprising clamping members which fold over the return bend, and provided with clasps to engage the ends of the tubes, said clasps forming split rings to fit around the ends of the tubes and to allow said collar-like portions to rest on said shoulders.

3. A connecting device for flanged or upset tubes, comprising a removable tubular element for establishing communication between two tubes, a housing mounted on the tubes and composed of two separate and distinct main parts or shackles, each of which comprises a sectional tube surrounding portion divided longitudinally and provided with an integral shoulder that bears against a shoulder on the tube which said portion surrounds, a retaining means for said tubular element carried by integral extensions on the sections of said tube surrounding portions, and means for preventing the sections of said tube surrounding portions from separating.

4. In a refinery apparatus, a return bend, a pair of shouldered tubes communicating therewith, a four part housing therefor, comprising complementary sections each of which is adapted to partially encircle the ends of said tubes and to be locked to the shoulders on the tubes, detachable means mounted in said housing sections to hold said tubes and return bend in a tight joint.

5. In a refinery apparatus, a return bend, a pair of shouldered tubes communicating therewith, a compound housing therefor, comprising complementary sections each adapted to partially encircle the ends of said tubes and to be locked to the shoulders on the tubes, detachable means mounted in said housing sections to hold said tubes and return bend in a tight joint, and means to hold said housing sections together.

6. In a refinery apparatus, a return bend, a pair of shouldered tubes communicating therewith, a

compound housing therefor, comprising complementary sections each adapted to partially encircle the ends of said tubes and to be locked to the shoulders on the tubes, detachable means mounted in said housing sections to hold said tubes and return bend in a tight joint, extensions on said housing sections which contact said tubes and securing means to contact said extensions and hold said sections together.

'7. In a refinery apparatus, a return bend, a pair of shouldered tubes communicating therewith, a compound housing therefor, comprising complementary sections each adapted to partially encircle the ends of said tubes and to be locked to the shoulders on the tubes, detachable means mounted in said housing sections to hold said tubes and return bend in a tight joint, each section having a downwardly extending substantially semi-cylindrical projection formed integral therewith and means for holding said sections together.

8. In a. refinery apparatus, a return bend adapted to connect a pair of shouldered tubes, a compound housing therefor, comprising complemen-' tary housing sections having arcuate flanges each adapted to be locked to the shoulders on the tubes, detachable means mounted in said sections to engage said return bend and means for holding the sections together.

ANDREW T. DUDLEY. 

